I think we might need an idea of numbers, and a rough budget.
Are you brave enough for a house or garden party?
If you've got room for a garden party you could have a theme, hire a dj, fire pits, barbecue, tents.
If money really is no object you could hire a club or a bar, or go for the cheaper option of hiring a room somewhere and doing any catering yourself.
Hire out a cinema, providing popcorn and so on.
You could take a big group of friends for an experience - Snozone or GoApe or similar.
Makeovers at a beauty salon - they usually create a party atmosphere with non-alcoholic cocktails and food.
Giant picnic in the park with games.
ummmm...still thinking...